Heat-resistant superalloy

ABSTRACT

A heat-resistant superalloy having chromium, aluminum, cobalt, titanium, and ruthenium added thereto as main components, and having a subcomponent(s) optionally added thereto, the remainder, excluding the main components and the subcomponent(s), comprising nickel and an impurity inevitably contained,
         wherein the amount of the chromium added is 2 to 25% by mass,   the amount of the aluminum added is 0.2 to 7% by mass,   the amount of the cobalt added is 19.5 to 55% by mass,   the amount of the titanium added is [0.17×(% by mass for cobalt−23)+3] to [0.17×(% by mass for cobalt−20)+7] % by mass (with the proviso that the amount of the titanium added is 5.1% by mass or more), and   the amount of the ruthenium added is 0.1 to 10% by mass.

TECHNICAL FIELD

The present invention relates to a heat-resistant superalloy used in aheat-resistant member for use in aircraft engine, generator gas turbine,or the like, particularly used in a turbine disk, a turbine blade, orthe like.

BACKGROUND ART

A turbine disk, which is a heat-resistant member for use in aircraftengine, generator gas turbine, or the like, is a part which supports amoving blade and rotates at a high speed. Therefore, the turbine diskrequires a material which endures a very large centrifugal stress andwhich is excellent in fatigue strength, creep strength, and fracturetoughness. On the other hand, as the engine and generator are beingimproved in the fuel consumption rate and performance, there are demandsthat the engine gas temperature should be improved and that the turbinedisk should be reduced in weight, and therefore the material for turbinedisk is required to have higher heat resistance and higher strength.

Generally, a Ni-based forging alloy is used in the turbine disk, and,for example, Inconel 718 utilizing a γ″ (gamma double prime) phase as astrengthening phase and Waspaloy having a γ′ (gamma prime) phase, whichis more stable than the γ″ phase, deposited in an amount of about 25 vol% and utilizing the γ′ phase as a strengthening phase have been widelyused. Further, from the viewpoint of dealing with an increase of thetemperature, Udimet 720 developed by Special Metals has been introducedsince 1986. Udimet 720 has a γ′ phase deposited in an amount of about 45vol % and has tungsten added for strengthening the solid solution of yphase, and exhibits excellent heat resistance properties. Udimet 720,meanwhile, has poor structure stability such that a detrimental TCP(topologically close packed) phase is formed in the Udimet 720 beingused. Therefore, Udimit 720Li (U720Li/U720LI) has been developed byimproving Udimet 720, e.g., reducing the chromium content. In Udimit720Li, however, a TCP phase is inevitably formed, and the use of Udimit720Li for a long time or at high temperatures is limited. Further, withrespect to Udimit 720 and Udimit 720 Li, a difference between the γ′solvus temperature and the initial melting temperature is small, and thenarrow process window for hot processing, heat treatment, or the likehas been pointed out. Thus, Udimit 720 and Udimit 720 Li have apractical problem in that it is difficult to produce a homogeneousturbine disk from them by a casting or forging process.

Powder metallurgy alloys, including AF115, N18, and Rene 88DT asrepresentative examples, are sometimes used in a high-pressure turbinedisk required to have a high strength. The powder metallurgy alloys havemerit in that a homogeneous disk having almost no segregation despitecontaining strengthening elements in a large amount can be obtained. Onthe other hand, the powder metallurgy alloys pose a problem in that, forpreventing contaminants from mixing into the alloy, a thorough controlof the production process, e.g., vacuum dissolution with high cleannessor optimal selection of the mesh size for powder classification isrequired, increasing the cost.

By the way, with respect to conventional Ni-based heat-resistantsuperalloys, a number of improvements of the chemical compositions havebeen proposed. The heat-resistant superalloys having improved chemicalcompositions have cobalt, chromium, and molybdenum, or molybdenum,tungsten, aluminum, and titanium added thereto as main components, andrepresentative examples of such superalloys include those having one ofor both of niobium and tantalum as essential components. However, thesechemical compositions are suitable for powder metallurgy, but makecasting or forging of the superalloy difficult. Further, the amount ofthe cobalt added to the heat-resistant superalloy is relatively large,but, taking into consideration the cost and the like, the amount of thecobalt added was limited to 23% by mass or less, excluding a specificcase.

Titanium has a function of strengthening the γ′ phase and is effectivein improving the tensile strength or crack propagation resistance, andtherefore titanium is added to the heat-resistant superalloy. However,the addition of titanium in an excess amount increases the γ′ solvustemperature, and further forms a detrimental phase, making it difficultto obtain a sound γ′ structure. From the viewpoint of avoiding this, theamount of the titanium added to the heat-resistant superalloy waslimited to about 5% by mass.

The present inventors have found that by positively adding cobalt in anamount of up to 55% by mass, the formation of a detrimental TCP phasecan be suppressed, and that by increasing both cobalt and titanium in apredetermined proportion, the γ/γ′ two-phase structure can bestabilized, and have proposed a heat-resistant superalloy which canendure for a long time even in a higher temperature region.

-   Patent document 1: Japanese Patent No. 2666911-   Patent document 2: Japanese Patent No. 3145091-   Patent document 3: Japanese Patent No. 3233361-   Patent document 4: Japanese Patent No. 4026883-   Patent document 5: WO2006/059805 pamphlet

DISCLOSURE OF THE INVENTION Problems that the Invention is to Solve

The above-mentioned heat-resistant superalloy already proposed by thepresent inventors has both cobalt and titanium increased in apredetermined proportion and is a novel alloy having excellent heatresistance. With respect to this heat-resistant superalloy, however, ithas additionally been found that when titanium is added in too large anamount, an η phase (Ni₃Ti) is likely to be formed in the heat-resistantsuperalloy. The η phase is in a plate form and causes the ductility ofthe heat-resistant superalloy around at room temperature to be poor.Further, the η phase is also in a cell form and causes the notchedstress rupture strength of the heat-resistant superalloy to lower.Therefore, the development of a heat-resistant superalloy having a goodbalance between excellent heat resistance and easy processing propertiesand having high reliability is strongly desired.

Means for Solving the Problems

The present inventors have made extensive and intensive studies ontechnical means for controlling the formation of the above-mentioned ηphase. As a result, it has been newly found that the addition ofruthenium to the heat-resistant superalloy proposed by the presentinventor exhibits a remarkably effect of suppressing the formation of anη phase in the superalloy, and the present invention has been completed,based on the above novel finding.

For solving the above problems, the heat-resistant superalloy of theinvention is a heat-resistant superalloy having chromium, aluminum,cobalt, titanium, and ruthenium added thereto as main components, andhaving a subcomponent(s) optionally added thereto, the remainder,excluding the main components and the subcomponent(s), comprising nickeland an impurity inevitably contained,

wherein the heat-resistant superalloy is characterized in that:

the amount of the chromium added is 2 to 25% by mass,

the amount of the aluminum added is 0.2 to 7% by mass,

the amount of the cobalt added is 19.5 to 55% by mass,

the amount of the titanium added is [0.17×(% by mass for cobalt−23)+3]to [0.17×(% by mass for cobalt−20)+7] % by mass (with the proviso thatthe amount of the titanium added is 5.1% by mass or more), and

the amount of the ruthenium added is 0.1 to 10% by mass.

In the heat-resistant superalloy, it is preferred that the amount of thetitanium added is [0.17×(% by mass for cobalt−23)+3] to [0.17×(% by massfor cobalt−20) +7] % by mass (with the proviso that the amount of thetitanium added is 5.3 to 11% by mass), and at least one of molybdenumand tungsten is added as the subcomponent,

wherein the amount of the molybdenum added is 5% by mass or less, andthe amount of the tungsten added is 5% by mass or less.

Further, in the heat-resistant superalloy, it is preferred that at leastone of zirconium, carbon, and boron is added as the subcomponent,

wherein the amount of the zirconium added is 0.01 to 0.2% by mass,

the amount of the carbon added is 0.01 to 0.15% by mass, and

the amount of the boron added is 0.005 to 0.1% by mass.

Further, in the heat-resistant superalloy, it is preferred that at leastone of molybdenum and tungsten and at least one of zirconium, carbon,and boron are added as the subcomponents,

wherein the amount of the molybdenum added is 5% by mass or less,

the amount of the tungsten added is 5% by mass or less,

the amount of the zirconium added is 0.01 to 0.2%by mass,

the amount of the carbon added is 0.01 to 0.15% by mass, and

the amount of the boron added is 0.005 to 0.1% by mass.

Further, in the heat-resistant superalloy, it is preferred that at leastone of molybdenum and tungsten, at least one of tantalum and niobium,and at least one of zirconium, carbon, and boron are added as thesubcomponents,

wherein the amount of the molybdenum added is 5% by mass or less,

the amount of the tungsten added is 5% by mass or less,

the amount of the tantalum added is 2% by mass or less,

the amount of the niobium added is 2% by mass or less,

the amount of the zirconium added is 0.01 to 0.2% by mass,

the amount of the carbon added is 0.01 to 0.15% by mass, and

the amount of the boron added is 0.005 to 0.1% by mass.

Further, in the heat-resistant superalloy, it is preferred that theamount of the cobalt added is 23.1 to 55% by mass.

Further, in the heat-resistant superalloy, it is preferred that theamount of the titanium added is [0.17×(% by mass for cobalt−23) +3] to[0.17×(% by mass for cobalt−20) +7] % by mass (with the proviso that theamount of the titanium added is 5.1 to 11% by mass).

Further, in the heat-resistant superalloy, it is preferred that theamount of the ruthenium added is 0.1 to 7% by mass.

Further, in the heat-resistant superalloy, it is preferred that theamount of the titanium added is [0.17×(% by mass for cobalt−23)+3] to[0.17×(% by mass for cobalt−20)+7] % by mass (with the proviso that theamount of the titanium added is 5.3 to 10% by mass), and the amount ofthe ruthenium added is 0.1 to 5% by mass.

Further, in the heat-resistant superalloy, it is preferred that theamount of the zirconium added is 0.01 to 0.15% by mass, the amount ofthe carbon added is 0.01 to 0.1% by mass, and the amount of the boronadded is 0.005 to 0.05% by mass.

Further, it is preferred that the heat-resistant superalloy contains noη phase in the alloy phase. The heat-resistant superalloy member of theinvention is characterized in that the member is produced from the aboveheat-resistant superalloy by at least one of casting, forging, andpowder metallurgy.

Advantage of the Invention

In the invention, there is provided a heat-resistant superalloy having agood balance between excellent heat resistance and easy processingproperties and having high reliability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows photomicrographs of the microstructures observed withrespect to the comparative alloy 2 (A) and the invention alloy 4 (B)obtained by adding ruthenium in an amount of 4% by mass to thecomparative alloy 2, which alloys have been subjected to casting.

FIG. 2 shows XRD diffraction patterns measured with respect to theinvention alloy 4 and comparative alloy 2, which have been subjected toaging treatment at 1,140° C. for 100 hours.

FIG. 3 shows photomicrographs of the microstructures observed withrespect to the invention alloy 4 {(B) and (D)} and the comparative alloy2 {(A) and (C)}, which have been subjected to heat treatment at 1,220°C. for one hour, and then subjected to aging at 1,140° C. for 32 hours{(A) and (B)} and for 100 hours {(C) and (D)}.

FIG. 4 shows TTT curves (time-temperature-transformation curves) for theformation of an η phase with respect to the following four types ofheat-resistant superalloys: (A) comparative alloy 1; (B) invention alloy3 (comparative alloy 1+2.5% by mass Ru); (C) comparative alloy 2; and(D) invention alloy 4 (comparative alloy 2+4% by mass Ru).

FIG. 5 shows photographs of the appearance of the comparative alloy 2(A) and invention alloy 4 (B), which have been subjected tohigh-temperature forging at 1,100° C. and at 0.1 s⁻¹.

MODE FOR CARRYING OUT THE INVENTION

In the invention, as already proposed, the contents of cobalt andtitanium in the heat-resistant superalloy are appropriately controlledto achieve excellent heat resistance, and further ruthenium is added tothe heat-resistant superalloy to thoroughly suppress the formation of anη phase which causes a problem in the processability of the superalloy,improving the processability, and thus a heat-resistant superalloyhaving a good balance between a heat resistance and easy processingproperties is provided.

Ruthenium (Ru) is a component capable of suppressing the formation of aTCP phase, and can improve the creep characteristics of theheat-resistant superalloy at high temperatures. This effect isremarkable when the amount of the ruthenium added to the heat-resistantsuperalloy is in the range of from 0.1 to 10% by mass. Taking intoconsideration the fact that ruthenium is an expensive metal and thebalance between a heat resistance and easy processing properties, theamount of the ruthenium added is preferably in the range of from 0.1 to7% by mass, more preferably from 0.1 to 5% by mass.

Cobalt (Co) is a component effective in controlling the solvustemperature of the γ′ phase, and when the amount of the cobalt added tothe heat-resistant superalloy is increased, the solvus temperature islowered to widen the process window, so that an effect of improving thesuperalloy in forging properties can also be obtained. In addition,cobalt suppresses the formation of a TCP phase to improve thehigh-temperature strength of the heat-resistant superalloy, andtherefore cobalt is positively added to the heat-resistant superalloy inan amount of 19.5% by mass or more. By virtue of the addition of cobaltin such an amount, there is achieved a practical heat-resistantsuperalloy having a good balance between a heat resistance and easyprocessing properties even in the region of composition in which theamount of the titanium (Ti) added is 5.1% by mass or more.

When cobalt and titanium are added in combination, for example, in theform of a Co—Ti alloy, it is preferred that the amounts of the cobaltand titanium added are determined in accordance with the below-mentionedformula for the range of the amount of the titanium added. When cobaltis added in an amount of 19.5% by mass or more, and even when cobalt isadded in an amount of 23.1% by mass or more, or an amount of up to 55%by mass, the above-mentioned heat-resistant superalloy can be similarlyobtained. In this connection, it is noted that, according to the resultsof a high-temperature compression test, an alloy having cobalt added inan amount of more than 55% by mass tends to be reduced in the strengthat up to 750° C. Therefore, generally, the amount of the cobalt added tothe heat-resistant superalloy is preferably 55% by mass or less, morepreferably 22 to 35% by mass, further preferably 23.1 to 35% by mass.

Titanium is added for strengthening the γ′ to improve the strength ofthe heat-resistant superalloy, and is required to be added in an amountof 5.1% by mass or more. When titanium and cobalt are added incombination, excellent phase stability is realized, thus achieving theheat-resistant superalloy having high strength. Basically, whenselecting, for example, a Co+Co₃Ti alloy which is a heat-resistantsuperalloy having a γ+γ′ two-phase structure, the addition of titaniumachieves a heat-resistant superalloy having a stable structure even in ahigh alloy concentration and having high strength. With respect to theamount of the titanium added to the heat-resistant superalloy, the lowerlimit is 5.1% by mass, and further the amount of the titanium added iswithin the range represented by the following formula:

[0.17×(% by mass for cobalt−23)+3] to [0.17×(% by mass forcobalt−20)+7].

On the other hand, when the amount of the titanium added is more than15% by mass, the formation of an η phase which is a detrimental phase,or the like may be marked, and therefore the amount of the titaniumadded is preferably 15% by mass or less. It is more preferred that theamount of the titanium added satisfies the above-mentioned formula forthe range and further is 5.1 to 15% by mass, advantageously 5.3 to 11%by mass, further advantageously 5.3 to 10% by mass.

Chromium (Cr) is added for improving the environmental resistance orfatigue crack propagation characteristics of the heat-resistantsuperalloy. The amount of the chromium added to the heat-resistantsuperalloy is in the range of from 2 to 25% by mass. When the amount ofthe chromium added is less than 2% by mass, desired properties cannot beobtained. When the amount of the chromium added is more than 25% bymass, a detrimental TCP phase is likely to be formed. The amount of thechromium added is preferably 5 to 20% by mass, more preferably 10 to 18%by mass.

Aluminum (Al) is an element which forms a γ′ phase, and the amount ofthe aluminum added to the heat-resistant superalloy is in the range offrom 0.2 to 7% by mass so that the γ′ phase is formed in an appropriateamount. The ratio of the titanium and aluminum contained in theheat-resistant superalloy affects the formation of an η phase andtherefore, for suppressing the formation of a TCP phase which is adetrimental phase, the amount of the aluminum added is preferably aslarge as possible within the above-mentioned range.

Tungsten (W) is a component effective in dissolving in the y phase andγ′ phase and strengthening the both phases to improve thehigh-temperature strength of the heat-resistant superalloy. When theamount of the tungsten added to the heat-resistant superalloy is toosmall, the resultant superalloy is likely to have unsatisfactory creepcharacteristics. On the other hand, when the amount of the tungstenadded is too large, the resultant superalloy has an excessivelyincreased alloy density and is disadvantageous from a practical point ofview. The amount of the tungsten added is generally 5% by mass or less.

Molybdenum (Mo) is a component effective in strengthening mainly the yphase to improve the creep characteristics of the heat-resistantsuperalloy. Molybdenum, meanwhile, is an element having a high densitylike tungsten, and when the amount of the molybdenum added to theheat-resistant superalloy is too large, the resultant superalloy has anexcessively increased alloy density and is disadvantageous from apractical point of view. The amount of the molybdenum added is generally5% by mass or less, preferably 4% by mass or less.

Carbon (C) is a component effective in improving the ductility and creepcharacteristics of the heat-resistant superalloy at high temperatures.The amount of the carbon added to the heat-resistant superalloy isgenerally in the range of from 0.01 to 0.15% by mass, preferably in therange of from 0.01 to 0.1% by mass. Boron (B) is a component effectivein improving the creep characteristics at high temperatures, fatiguecharacteristics, and the like of the heat-resistant superalloy. Theamount of the boron added to the heat-resistant superalloy is generallyin the range of from 0.005 to 0.1% by mass, preferably in the range offrom 0.005 to 0.05% by mass. When the amounts of the carbon and boronadded exceed the above-mentioned respective predetermined ranges, it islikely that the creep strength of the heat-resistant superalloy islowered or the process window narrows. Zirconium (Zr) is a componenteffective in improving the ductility, fatigue characteristics, and thelike of the heat-resistant superalloy. The amount of the zirconium addedto the heat-resistant superalloy is generally in the range of from 0.01to 0.2% by mass, preferably in the range of from 0.01 to 0.15% by mass.

Examples of other components include tantalum (Ta), niobium (Nb),rhenium (Re), vanadium (V), hafnium (Hf), and magnesium (Mg), and thesecomponents can be added to the heat-resistant superalloy in such anappropriately controlled amount that the properties of theheat-resistant superalloy are not sacrificed.

Examples are shown below. The following Examples should not be construedas limiting the scope of the present invention.

Examples

Four types of invention alloys and two types of comparative alloys wereprepared by melting in a vacuum induction heating method. The chemicalcompositions of these alloys are shown in Table 1.

TABLE 1 Name of alloy Ni Co Cr Mo W Al Ti C B Zr Ru Comparative alloy 1Bal. 23.1 16.8 3.12 1.25 1.87 5.44 0.03 0.018 0.022 — Invention alloy 1Bal. 23.0 16.7 3.1 1.24 1.86 5.41 0.03 0.018 0.022 0.5 Invention alloy 2Bal. 22.8 16.5 3.07 1.23 1.84 5.36 0.03 0.018 0.022 1.5 Invention alloy3 Bal. 22.5 16.4 3.04 1.22 1.82 5.30 0.03 0.018 0.022 2.5 Comparativealloy 2 Bal. 28.6 12.8 2.4 1.0 2.0 7.4 0.03 0.01 0.02 — Invention alloy4 Bal. 27.5 12.3 2.3 0.96 1.92 7.1 0.03 0.01 0.02 4 * Each elementalcomposition is indicated by “% by mass”.

In all the invention alloys, the formation of a TCP phase which is adetrimental phase, especially the formation of an η phase (Ni₃Ti) wassuppressed, and the improvement effect for the stability of themicrostructure by the addition of ruthenium was recognized. For example,as shown in FIG. 1, in the cast alloy of the comparative alloy 2 (A),the formation of an η phase was found on the grain boundary, whereas, inthe invention alloy 4 (B) obtained by adding ruthenium in an amount of4% by mass to the comparative alloy 2, the formation of an η phase wasnot recognized. With respect to these two alloys, the stability of themicrostructure in a heat treatment was evaluated. Specifically, the twoalloys were individually subjected to heating treatment at 1,220° C. forone hour, and then cooled with water, and subsequently, subjected toaging treatment in a temperature region of from 700 to 1,200° C. for 1to 1,000 hours. FIG. 2 shows X-ray diffraction patterns of the twoalloys which have been subjected to aging treatment at 1,140° C. for 100hours. In the comparative alloy 2 which has been subjected to agingtreatment, diffraction peaks ascribed to the η phase as well as the yphase and γ′ phase were observed, but, in the invention alloy 4 havingruthenium added in an amount of 4% by mass, contrary to the comparativealloy 2, a diffraction peak ascribed to the η phase was not observed.

FIG. 3 shows photomicrographs of the microstructures observed withrespect to the invention alloy 4 and comparative alloy 2, which havebeen subjected to heat treatment at 1,220° C. for one hour and thensubjected to aging treatment at 1,140° C. for 32 hours and for 100hours. As can be seen from the photomicrographs, in the comparativealloy 2 {(A) and (C)}, a number of η phases in a plate form having asize of several hundred microns were observed, which are not observed inthe invention alloy 4 {(B) and (D)}. These results clearly show theremarkable effect achieved by the addition of ruthenium in theheat-resistant superalloy of the invention.

Table 2 shows the results of the measurement of a compressive stress atyield and a compressive creep at 725° C/630 MPa with respect to theinvention alloys and comparative alloys shown in Table 1.

TABLE 2 Compressive stress at yield (MPa) Compressive creep (s⁻¹) Nameof alloy 25° C. 400° C. 700° C. 800° C. 1000° C. 725° C./630 MPaComparative alloy 1 873 864 861 847 340 5.21 × 10⁻⁸ Invention alloy 1890 886 881 859 344 3.27 × 10⁻⁸ Invention alloy 2 894 867 859 848 3401.85 × 10⁻⁸ Invention alloy 3 868 861 842 828 335 1.71 × 10⁻⁸Comparative alloy 2 929 923 920 916 341 1.35 × 10⁻⁸ Invention alloy 4917 915 911 911 358 1.19 × 10⁻⁸

The results shown in Table 2 are those measured with respect to theinvention alloys and comparative alloys, which have been subjected toheat treatment at 1,100° C. for 4 hours and air cooling, and thensubjected to aging treatment at 650° C. for 24 hours and at 760° C. for16 hours. The compression test was conducted using a tester (SHIMAZUAG5OKNI), manufactured by Shimadzu Corporation, in a temperature regionof from room temperature to 1,000° C. at an apparent strain rate of3×10⁻⁴ s⁻¹. The invention alloys have a compressive stress at yieldsubstantially equivalent to that of the comparative alloys, and theseresults indicate that the addition of ruthenium does not adverselyaffect the compressive stress at yield of the alloy. Further, in some ofthe invention alloys, an effect such that the addition of rutheniumimproves the performance is also recognized. Particularly, in theinvention alloy 3 obtained by adding ruthenium in an amount of 2.5% bymass to the comparative alloy 1, the compressive creep is drasticallyimproved from 5.2×10⁻⁸s⁻¹ to 1.71×10⁻⁸ s⁻¹. Accordingly, the resultsshown in Table 2 suggest that the addition of ruthenium in theheat-resistant superalloy of the invention achieves an effect such thatthe processability of the heat-resistant superalloy is remarkablyimproved without sacrificing the heat resistance.

FIG. 4 shows the suppression effect for the η phase formation in theinvention alloy having ruthenium added thereto. FIGS. 4(A) and 4(C) showTTT curves (time-temperature-transition curves) for the formation of anη phase with respect to the comparative alloys 1 and 2, respectively.The TTT curves of the comparative alloys 1 and 2 had a C-shape, and thenose temperature and the temperature range in which the presence of an ηphase is recognized were about 1,000° C. and the range of from 1,100 to1,150° C., respectively, with respect to the comparative alloy 1, andabout 1,170° C. and the range of from 850 to 1,200° C., respectively,with respect to the comparative alloy 2. That is, in each of thecomparative alloys 1 and 2, 1₁ phases are present in a wide range (theregion in which symbols * are present). In contrast, as shown in FIGS.4(B) and 4(D), in each of the invention alloys 3 and 4, the formation ofan η phase was not recognized in any region. These results clearly showthat the addition of ruthenium in the heat-resistant superalloy of theinvention remarkably improves the stability of the phase.

An existing disk alloy, such as U720L1, is generally subjected tohigh-temperature forging at about 1,100° C., and the deformability of analloy in a similar temperature region is an important factor inpresuming the workability of the alloy in the processing. Using theinvention alloy 4 and comparative alloy 2, workability was evaluated bya high-temperature compression test with respect to each of thesealloys. The evaluation of the workability was conducted at 1,100° C. andat a strain rate of 0.1 s⁻¹. Each of the alloys was maintained at thetemperature for the measurement for 10 minutes so that the alloy becamehomogeneous, and then a strain of 0.65 was applied to the alloy toeffect deformation, followed by rapid cooling using water. As shown inFIG. 5, in the comparative alloy 2 containing an η phase, large cracksare caused, which confirms that the workability is very poor. Bycontrast, in the invention alloy 4 having ruthenium added thereto, onlyslight cracks are observed in the outermost shell, and, from this, it isconsidered that the ruthenium added to the alloy suppresses theformation of an η phase, remarkably improving the workability in thehigh-temperature forging processing.

INDUSTRIAL APPLICABILITY

The heat-resistant superalloy of the invention has a good balancebetween excellent heat resistance and easy processing properties, andhas high reliability and is used in a heat-resistant member for use inaircraft engine, generator gas turbine, or the like, particularly usedin a turbine disk, a turbine blade, or the like.

1. A heat-resistant superalloy having chromium, aluminum, cobalt,titanium, and ruthenium added thereto as main components, and having asubcomponent(s) optionally added thereto, the remainder, excluding themain components and the subcomponent(s), comprising nickel and animpurity inevitably contained, the heat-resistant superalloy beingcharacterized in that: the amount of the chromium added is 2 to 25% bymass, the amount of the aluminum added is 0.2 to 7% by mass, the amountof the cobalt added is 19.5 to 55% by mass, the amount of the titaniumadded is [0.17×(% by mass for cobalt−23)+3] to [0.17×(% by mass forcobalt−20)+7] % by mass (with the proviso that the amount of thetitanium added is 5.1% by mass or more), and the amount of the rutheniumadded is 0.1 to 10% by mass.
 2. The heat-resistant superalloy accordingto claim 1, characterized in that the amount of the titanium added is[0.17×(% by mass for cobalt−23)+3] to [0.17×(% by mass forcobalt−20)+7]% by mass (with the proviso that the amount of the titaniumadded is 5.3 to 11% by mass), and at least one of molybdenum andtungsten is added as the subcomponent, wherein the amount of themolybdenum added is 5% by mass or less, and the amount of the tungstenadded is 5% by mass or less.
 3. The heat-resistant superalloy accordingto claim 1, characterized in that at least one of zirconium, carbon, andboron is added as the subcomponent, wherein the amount of the zirconiumadded is 0.01 to 0.2% by mass, the amount of the carbon added is 0.01 to0.15% by mass, and the amount of the boron added is 0.005 to 0.1% bymass.
 4. The heat-resistant superalloy according to claim 1,characterized in that at least one of molybdenum and tungsten and atleast one of zirconium, carbon, and boron are added as thesubcomponents, wherein the amount of the molybdenum added is 5% by massor less, the amount of the tungsten added is 5% by mass or less, theamount of the zirconium added is 0.01 to 0.2% by mass, the amount of thecarbon added is 0.01 to 0.15% by mass, and the amount of the boron addedis 0.005 to 0.1% by mass.
 5. The heat-resistant superalloy according toclaim 1, characterized in that at least one of molybdenum and tungsten,at least one of tantalum and niobium, and at least one of zirconium,carbon, and boron are added as the subcomponents, wherein the amount ofthe molybdenum added is 5% by mass or less, the amount of the tungstenadded is 5% by mass or less, the amount of the tantalum added is 2% bymass or less, the amount of the niobium added is 2% by mass or less, theamount of the zirconium added is 0.01 to 0.2% by mass, the amount of thecarbon added is 0.01 to 0.15% by mass, and the amount of the boron addedis 0.005 to 0.1% by mass.
 6. The heat-resistant superalloy according toany one of claims 1 to 5 claim 1, characterized in that the amount ofthe cobalt added is 23.1 to 55% by mass.
 7. The heat-resistantsuperalloy according to claim 1, characterized in that the amount of thetitanium added is [0.17×(% by mass for cobalt−23)+3] to [0.17×(% by massfor cobalt−20)+7] % by mass (with the proviso that the amount of thetitanium added is 5.1 to 11% by mass).
 8. The heat-resistant superalloyaccording to claim 1, characterized in that the amount of the rutheniumadded is 0.1 to 7% by mass.
 9. The heat-resistant superalloy accordingto claim 1, characterized in that the amount of the titanium added is[0.17×(% by mass for cobalt−23)+3] to [0.17×(% by mass for cobalt−20)+7]% by mass (with the proviso that the amount of the titanium added is 5.3to 10% by mass), and the amount of the ruthenium added is 0.1 to 5% bymass.
 10. The heat-resistant superalloy according to claim 3,characterized in that the amount of the zirconium added is 0.01 to 0.15%by mass, the amount of the carbon added is 0.01 to 0.1% by mass, and theamount of the boron added is 0.005 to 0.05% by mass.
 11. Theheat-resistant superalloy according to claim 1, characterized bycontaining no η phase in the alloy phase.
 12. A heat-resistantsuperalloy member characterized in that the member is produced from theheat-resistant superalloy according to claim 1 by at least one ofcasting, forging, and powder metallurgy.